Clot retrieval system for removing occlusive clot from a blood vessel

ABSTRACT

A clot retrieval device comprising an elongate shaft having a proximal end and a distal end and a clot retrieval element at the distal end of the elongate shaft. A proximal end of the elongate shaft configured to retract a first catheter over the elongate shaft. The shaft extension member comprising one or more raised profiles configured to interfere with one or more indentations along the elongate shaft such that the shaft extension member is configured to extend between a first length and an intermediate length. A second catheter is advanced to or adjacent to the distal end of the clot retrieval device shaft to enable enhanced aspiration adjacent to the clot retrieval element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser. No. 16/372,876, filed Apr. 2, 2019, which is a Divisional application of U.S. application Ser. No. 14/644,685, filed Mar. 11, 2015 which claims the benefit of U.S. Provisional Application No. 61/951,270, filed Mar. 11, 2014, each of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to devices and methods of removing acute blockages from blood vessels. The invention especially relates to removing acute obstructions from blood vessels. Acute obstructions may include clot, misplaced devices, migrated devices, large emboli and the like. Thromboembolism occurs when part or all of a thrombus breaks away from the blood vessel wall. This clot (now called an embolus) is then carried in the direction of blood flow. An ischemic stroke may result if the clot lodges in the cerebral vasculature. A pulmonary embolism may result if the clot originates in the venous system or in the right side of the heart and lodges in a pulmonary artery or branch thereof. Clots may also develop and block vessels locally without being released in the form of an embolus—this mechanism is common in the formation of coronary blockages and can also occur in the cerebral vasculature.

BACKGROUND

There are significant challenges associated with designing clot removal systems that can deliver high levels of performance:

There are a number of access challenges that make it difficult to deliver devices. In cases where access involves navigating the aortic arch (such as coronary or cerebral blockages) the configuration of the arch in some patients makes it difficult to position a guide catheter. These difficult arch configurations are classified as either type 2 or type 3 aortic arches with type 3 arches presenting the most difficulty. The tortuosity challenge is even more severe in the arteries approaching the brain. For example it is not unusual at the distal end of the internal carotid artery that the device will have to navigate a vessel segment with a 180° bend, a 90° bend and a 360° bend in quick succession over a few centimetres of vessel. In the case of pulmonary embolisms, access may be gained through the venous system and then through the right atrium and ventricle of the heart. The right ventricular outflow tract and pulmonary arteries are delicate vessels that can easily be damaged by inflexible or high profile devices. For these reasons it is desirable that the clot retrieval device be compatible with as low profile and flexible access and support catheters as possible.

The vasculature in the area in which the clot may be lodged is often fragile and delicate. For example neurovascular vessels are more fragile than similarly sized vessels in other parts of the body and are in a soft tissue bed. Excessive tensile forces applied on these vessels could result in perforations and hemorrhage. Pulmonary vessels are larger than those of the cerebral vasculature, but are also delicate in nature, particularly those more distal vessels.

The clot may comprise any of a range of morphologies and consistencies. Long strands of softer clot material may tend to lodge at bifurcations or trifurcations, resulting in multiple vessels being simultaneously occluded over significant lengths. More mature and organized clot material is likely to be less compressible than softer fresher clot, and under the action of blood pressure it may distend the compliant vessel in which it is lodged. Furthermore the inventors have discovered that the properties of the clot may be significantly changed by the action of the devices interacting with it. In particular compression of blood clot causes dehydration of the clot and results in a dramatic increase in both clot stiffness and coefficient of friction.

The clots may not only range in shape and consistency, but also may vary greatly in length, even in any one given area of the anatomy. For example clots occluding the middle cerebral artery of an ischemic stroke patient may range from just a few millimetres to several centimetres in length.

In the case of an intracranial occlusion a variety of access routes are possible with known devices, including a direct stick into the carotid artery, a brachial approach, or a femoral access. Once access has been gained to the arterial system using conventional and well understood techniques, a guide catheter or long sheath is typically placed as close to the occlusive clot as practical. For example, In the case of a middle cerebral artery occlusion the guide catheter might be placed in the internal carotid artery proximal of the carotid siphon. A microcatheter is then advanced across clot, typically with the aid of a guidewire. In some cases an additional catheter (which may be known as a Distal Access Catheter or DAC) may be used in a triaxial system such that the microcatheter is advanced through the DAC, which is in turn advanced through the guide catheter or long sheath. Once the microcatheter tip has been advanced across and distal of the clot the guidewire is removed and the clot retrieval device is advanced through the microcatheter until it reaches its distal end. The microcatheter is then retracted, allowing the clot retrieval device to expand within and on either side of the clot.

A particular problem arises with known systems because of the multiple catheters/shafts required to be in place at various stages during the procedure. For example in many cases it is desirable to be able to aspirate (apply a suction force) through the guide/sheath or DAC to assist in the withdrawal of the clot. The effectiveness of this aspiration can be hindered by the presence of catheter shafts within the aspiration lumen, and it is therefore sometimes desirable to be able to remove the microcatheter prior to aspiration and clot retrieval. The vessels through which the catheters are passed are very narrow and in most cases very tortuous. Thus, the anatomy presents major challenges to removing or advancing further devices or catheters that may be required during a procedure, as clot retrieval device shafts are typically not exchange length.

In general, there is a need to provide a clot retrieval system which provides the required flexibility to a physician to deal with a wide range of clots, often in an emergency situation.

STATEMENT OF THE INVENTION

According to the invention there is provided a clot retrieval device comprising an elongate shaft having a proximal end and a distal end; and a clot retrieval element at the distal end of the elongate shaft, a proximal end of the elongate shaft of the clot retrieval device being adapted for retraction of a first catheter over said clot retrieval device elongate shaft, a second catheter being advanced to or adjacent to the distal end of the clot retrieval device shaft to enable enhanced aspiration adjacent to the clot retrieval element.

In one embodiment aspiration is delivered through the second catheter, the lumen of the second catheter being larger than the lumen of the first catheter. The first catheter may comprise a microcatheter through which the clot retrieval device is delivered. In one case the second catheter an intermediate catheter.

In one case the proximal end of the shaft is adapted for retraction of a first catheter having a lumen and subsequent advancement of a second catheter having a lumen. In one case the lumen of the second catheter being larger than the lumen of the first catheter.

In one case the proximal end of the shaft is adapted for retraction and removal of a first catheter having a lumen through the second catheter.

In one embodiment the device comprises an adaptor at the proximal end of the elongate shaft, the adaptor being adapted to receive a shaft extension section.

The adaptor may be integral with the shaft proximal section. For example, the adaptor may comprise a receiver which is adapted to receive shaft extension section.

In another embodiment the adaptor is releasably mountable to the proximal end of the elongate shaft. The adaptor may comprise a mounting section for mounting to the proximal end of the shaft and a receiver which is adapted to receive a shaft extension section. In some cases, the adaptor mounting section is a push fit with the proximal end of the shaft. The adaptor receiver may be a push fit with a shaft extension.

The invention also provides a clot retrieval device of the invention and an adaptor for mounting to a proximal end of the elongate shaft of the clot retrieval device. The adaptor may comprise a mounting section for mounting to the proximal end of the shaft and a receiver which is adapted to receive a shaft extension section. The adaptor mounting section may be a push fit with the proximal end of the shaft. The adaptor receiver may be a push fit with a shaft extension.

In one embodiment the adaptor is configured to accept the proximal end of a standard guidewire. Thus, the guide wire that was initially used to aid advancement of the microcatheter can be used or re-used as a shaft extender.

In one case the clot retrieval device shaft has at least one tactile feature at/or adjacent to the proximal end thereof.

In one embodiment the clot retrieval device shaft has at least one high friction feature at/or adjacent to the proximal end thereof.

Also provided is a clot retrieval device wherein the shaft of the clot retrieval device is extendable. This concept could be applied to any endovascular medical device in which the extension of the device shaft is advantageous.

The proximal region of the device shaft may be tubular and a shaft extension member is movable from a retrieval configuration in which the extension member is within the proximal region to an extended configuration in which the extension member is at least partially extended proximally from the proximal region of the device shaft.

In one case the tubular proximal region and/or the extension member comprises at least one stop to set the length to which the extension member may extend from the tubular proximal region and/or to control the degree of push that may be applied to the extension member.

The invention also provides method for retrieving a clot from a vasculature comprising the steps of providing a clot retrieval device having a compressed or retracted delivery configuration and an expanded deployed configuration, the clot retrieval device having an elongate shaft; providing a first catheter; providing a second catheter; deploying the clot retrieval device at/or adjacent to the clot; and retracting the first catheter over the clot retrieval device shaft whilst maintaining control of the proximal end of the retrieval device shaft.

The method may comprise applying aspiration to the clot through the lumen of the second catheter after retraction of the first catheter over the retrieval device shaft.

In one case the first catheter is a delivery catheter for the clot retrieval device and the method comprises deploying the retrieval device from the delivery catheter and subsequently retracting the delivery catheter over the clot retrieval device shaft.

The method may comprise the step of extending the length of the retrieval device shaft prior to retraction of the first catheter.

In one case the method comprises the steps of connecting one end of an adaptor to the proximal end of the device shaft and connecting as proximal shaft extension to the other end of the adaptor. In one case the device shaft comprises an extension member and the method compresses the steps of moving the extension member from a retracted to an extended configuration prior to retraction of the first catheter.

The method may comprise the step of extending the length of the clot retrieval device shaft and delivering the second catheter over the extended length of the device shaft and distally towards the clot.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of a prior art clot retrieval system, in use;

FIGS. 2 and 3 are views of parts of the prior art clot retrieval system;

FIG. 4 is a view of a distal end of the prior art clot retrieval system;

FIG. 5 is a cross sectional view on the line V-V in FIG. 4 ;

FIGS. 6 and 7 are views of a clot retrieval system according to the invention;

FIG. 8 is a view of a distal end of the clot retrieval system of FIGS. 6 and 7 ;

FIG. 9 is a cross sectional view on the line IX-IX in FIG. 8 ;

FIG. 10 is another view of a clot retrieval system of the invention including an adaptor;

FIGS. 11 to 13 are view of various adaptors used in the invention;

FIGS. 14 and 15 are views of further adaptors used in the invention;

FIGS. 16 and 17 are views of parts of the clot retrieval system and adaptors, in use;

FIGS. 18 and 19 are views of further adaptors of the invention;

FIGS. 20 to 24 are views of a proximal section of a clot retrieval shaft with various proximal tactile features;

FIGS. 25 to 27 are views of proximal sections of clot retrieval shafts;

FIGS. 28 to 30 are views of various shaft extensions and adaptors of the invention;

FIGS. 31 a to 31 d are views of a clot retrieval device with an extendable shaft; and

FIGS. 32 a to 32 d are views of a method of use of a system of the invention.

DETAILED DESCRIPTION

Various devices and methods for removal of acute blockages from blood vessels are known. For example, various clot retrieval devices and methods of use are described in our WO2012/120490A and US2013-0345739A. The entire contents of all of the above-listed applications are herein incorporated by reference.

Known devices (FIGS. 1 to 5 ) generally comprise an elongate shaft 1 having a proximal end 2 and a distal end 3. A clot retrieval element 4 is mounted at the distal end of the elongate shaft. The clot retrieval element 4 may have a collapsed delivery configuration and an expanded deployed configuration. A microcatheter 5 is advanced across a clot with the aid of a guidewire. Once the microcatheter distal tip has been advanced across and distal of the clot the guide wire is removed and the clot retrieval element 4 and associated elongate shaft 1 is advanced through the microcatheter 5 in the collapsed delivery configuration. When the retrieval element 4 has crossed the clot through the microcatheter 5, the microcatheter 5 is then retracted, allowing the clot retrieval element 4 to expand within and on either side of the clot. In some cases a guide catheter 8 is first placed as close as possible to the occlusive clot as practical. The guide catheter 8 has a proximal connector 9 through which the microcatheter 5 is introduced. The microcatheter 5 has a proximal connector 10 through which the clot retrieval device is introduced through a connector 11. In some cases an additional catheter l2 with a proximal connector 13 (which may be known as a Distal Access Catheter or DAC) may be used in a triaxial system as illustrated in FIGS. 1 to 5 . In this case the microcatheter 5 is introduced through the DAC 12which in turn is advanced through the guide catheter 8.

As explained above, there is a very wide variation in clot type, location and size, all of which influence the optimum procedural steps required for clot retrieval. In order to provide the clinician with the flexibility to cope with all eventualities, in the invention the proximal end 2 of the elongate shaft 1 of the retrieval device is adapted so that a first catheter such as the microcatheter 5 can be retracted over the shaft 1 and removed whilst still retaining control over the clot retrieval element from the proximal end of the shaft 1 of the retrieval device. This is important in facilitating further procedures initiated as close as possible to the clot through the maximum possible lumen size. The difference in lumen size will be particularly apparent by comparing FIG. 5 (prior art) and FIG. 9 . FIGS. 5 and 9 are section view through FIGS. 4 and 8 respectively. In FIG. 9 the microcatheter is not obstructing the lumen of the additional catheter such as a DAC 12 so that the maximum lumen is available for example for aspiration and/or clot retrieval. For example, for a large clot or a clot which is difficult to dislodge, the second catheter may facilitate aspiration of the clot. Alternatively, or additionally, the second catheter may facilitate more close control over a dislodged clot so that it is contained within the second catheter as close as possible to the original clot location. This minimises the risk of clot fragments becoming mobile in a section of the vasculature proximal to the clot location.

It will be appreciated that in prior art systems it is not possible to remove the microcatheter whilst still retaining control over the clot retrieval element 4 via the retrieval device shaft 1—pulling the microcatheter 5 proximally will occlude the shaft 1 at the proximal end 2. This presents a problem to the physician as he needs to let go of and lose control of the clot retrieval device shaft in order to fully remove the microcatheter. This could result in the clot retrieval element moving proximally, which could result in loss of captured clot. One solution to this would be to provide a very long clot retrieval device shaft, but such shaft would need to be greater than 3.5 meters in length in order to ensure that the shaft never becomes occluded by the microcatheter. Such along shaft would be extremely cumbersome and would hinder the physician in cases where microcatheter removal was not required.

The inventors have discovered an adaption of the shaft length of the clot retrieval device that can be employed which allows safe microcatheter removal without adding a cumbersome length to the shaft 1. This shaft configuration is illustrated in FIGS. 6 and 7 , and provides an additional length 15 to the proximal end of the clot retrieval device shaft 1 which corresponds to the length of significant vascular tortuosity 16 proximal to the clot retrieval element 4. This additional length 15 allows the user to retain control of the clot retrieval device shaft 1 while retracting the microcatheter 5 through this distal tortuosity. Once the microcatheter tip is proximal of this tortuosity the frictional force between the clot retrieval device shaft 1 and the microcatheter 5 drops significantly. In the case of femoral access to the cerebral vasculature a microcatheter of approximately 1.5 m is typically employed, and the clot retrieval device shaft is typically approximately 1.9 m. This 1.9 m shaft length is required in order that the microcatheter 5 can be retracted a few cm proximal of the clot retrieval device to deploy the device, while still leaving exposed clot retrieval device shaft 1 proximal of the proximal end of the microcatheter, which is typically fitted with a rotating hemostasis valve of approximately 7 cm in length. Extending this shaft 1 to at least 2.1 m, but ideally not more than 2.3 m will allow for the microcatheter to be retracted from the relatively tortuous vessels distal of the aortic arch without loss of the shaft access (as illustrated in FIG. 7 ), and without excessive shaft length protruding off the end of the hospital trolley bed on which the patient is lying.

An alternative means of retaining shaft control while removing a microcatheter is to provide a shaft extension. Such an extension could be a dedicated extension supplied for that very purpose, or could (preferably) be an alternative use of a standard guidewire, such as the guidewire that was used to advance the microcatheter into position in the first place. Enabling a standard guidewire to be used for this purpose is particularly advantageous for emergency acute stroke clot retrieval cases, because speed of recanalisation is such a vital factor to good patient outcomes. If the physician can save even a few seconds in restoring flow to the brain this can have a significant impact on the end result for the patient. Also these procedures are unplanned and after happen late at night or in the early morning, when only a small team are on call and finding accessory devices or extension wire is not as easy as it might be with a full team in the day time.

One embodiment of such an extension would be approximately the length of the microcatheter, so that the user could retain full control of the clot retrieval device shaft during microcatheter removal. Another embodiment of such an extension would be much shorter—less than 60 cm in length, or even as short as 15 cm or 20 cm in length, so that the user can could retain full control of the clot retrieval device shaft during the retraction of the microcatheter through the region of maximum distal tortuosity, but then release the shaft for full removal of the microcatheter from the patient.

Referring for example to FIGS. 10 to 13 in one case an adaptor 20is provided which has a receiver 21 which is adapted to receive a shaft extension 25.

In some cases (for example FIG. 12 ) the adaptor 20 is integral with the proximal end of the shaft. In other cases (FIGS. 11, 13 ) the adaptor20 may be releasably mountable to the proximal end of the shaft.

Referring to FIGS. 14 to 17 in this case an adaptor 20 has amounting section 30 for mounting to the proximal end of the retrieval device shaft and a receiver 31 which is adapted to receive the shaft extension 25. Various designs are possible. The adaptor may be used to join the proximal end of the retrieval device shaft to a guidewire by a simple push fit (FIGS. 14 to 17 ). A mid to high modulus polymeric material with a high coefficient of friction may be used to provide a good interference fit. Alternatively (FIGS. 11 to 13 ) the adaptor may be of a metal such as nitinol or stainless steel or similar In this case the adaptor may have an engagement feature 40 such as a taper and/or a clip or spring feature to positively engage with the proximal end of the retrieval device shaft and/or the extension shaft 25.

Referring to FIGS. 18 to 19 there is illustrated an adaptor 50which in this case is configured to accept the proximal end 52 of a standard guide wire 51. In this case a guide wire 51 which was initially used to aid advancement of a microcatheter can now be used or re-used as a shaft extender.

Referring to FIGS. 20 to 24 in some embodiments tactile features such as bumps, grooves or surface indentations, raised areas or higher friction areas may be provided towards the proximal end of the elongate retrieval device shaft. These features can be used to provide two distinct benefits: 1) they can provide tactile feedback to the user to indicate when the clot retrieval element is approaching the distal end of the microcatheter. This means that the physician can advance the device quickly through the microcatheter without any need for x-ray guidance (minimizing exposure to both patient and medical team) until he feels these tactile features. He can then slow down and advance the device carefully over the last few centimetres using x-ray/fluoroscopic guidance. 2) they can be used to provide a higher friction, easier to grip area of shaft to help the physician to advance the device through the more tortuous vasculature that typically exists adjacent the clot. This is particularly helpful when there is significant tortuosity to be navigated, because in these cases a higher force must be exerted to advance the device shaft. It is important that the section of shaft that is passing through tortuosity has a low coefficient of friction, so these higher friction “grip” features are ideally positioned only on a proximal region of the shaft.

Where the above mentioned tactile features are used to provide an indication to the user as to the position of the clot retrieval element relative to the end of the microcatheter they may be provided over a distance of 3 to 10 cm, possibly about 5 cm at a location which is a fixed distance from the distal end of the device, where said fixed distance is slightly less than the length of the microcatheter and adapter (typically a rotating haemostasis valve). For typical neurovascular microcatheters a distance of between 1.5 m and 1.65 m is suitable.

Referring to FIGS. 25 to 27 there are illustrated three examples of profiles of the proximal end of the shaft of a clot retrieval device which are configured to mate with a receiving portion or adaptor at the end of a shaft extension member.

FIG. 25 shows the proximal region of shaft 100 which comprises an undulating section 100 terminating in proximal end 102. Undulating section 101 is designed to create an interference fit in an adaptor such as that shown in FIG. 28 , where the inner diameter 133 of adaptor 132 is smaller than the effective diameter of undulating section 101. Shaft 100 is preferably made from a relatively high modulus material such as stainless steel or Nitinol or other metal or alloy to provide the user with the means to transfer a push force through the shaft to its distal end. Shaft 100 may have an outer diameter of between 0.010″ and 0.030″, but preferably between 0.014″ and 0.020″ and most preferably between 0.016″ and 0.018″.

FIG. 26 shows the proximal region of shaft 110 which comprises a stepped proximal end with a reduced diameter section 111, a groove or channel 112 and a rounded proximal end 113. This shaft is configured to mate with adaptors of this invention such as the adaptor 142 shown in FIG. 29 , such that the indented spring arm 143 aligns with the recessed channel 112, creating a type of snap-fit joint that can be attached ordetached using a simple push or pull action.

FIG. 27 shows the proximal region of shaft 120 which comprises a reduced diameter section 121 and a tapered proximal end 122. This shaft is configured to mate with many of the previously disclosed adaptors of this invention and adaptors such as the adaptor 152 shown in FIG. 30 .

Referring to FIGS. 28 to 30 there are illustrated the distal portions of three examples of shaft extensions of this inventions incorporating adaptors configured to enable the extension to be attached to the proximal end of the shaft of a clot retrieval device.

FIG. 28 illustrates the distal portion of shaft extension 130, to which is attached adaptor 132. The distal end 131 of the shaft extension 130 is stepped down in diameter to fit within the lumen of adaptor 132 to which it is attached. This attachment may comprise a weld, a bond, an interference fit or other suitable attachment means. In one embodiment the extension and adaptor are made from a single piece of material (a monolithic structure). Adaptor 132 comprises a receiver 133 configured to mate with the proximal end of a shaft such as that shown in FIG. 25 , or any such shaft with which it can create an interference fit. The shaft extension 130 is preferably made from a relatively high modulus material such as stainless steel or Nitinol or other metal or alloy. Adaptor 132 is preferably made from a similar family of materials.

FIG. 29 illustrates the distal portion of shaft extension 140, to which is attached adaptor 142. The distal end 141 of the shaft extension140 is stepped down in diameter to fit within the lumen of adaptor 142 to which it is attached. This attachment may comprise a weld, a bond, an interference fit or other suitable attachment means. In one embodiment the extension and adaptor are made from a single piece of material (a monolithic structure). Adaptor 142 comprises an indented spring arm 143, which may be constructed but cutting slots 144 in a tubular member and providing an undulation or indentation 143 in the resultant arm of material. The shaft extension and adaptor materials may be similar to those described in relation to FIG. 28 above.

FIG. 30 illustrates the distal portion of shaft extension 150, to which is attached adaptor 152. The distal end 151 of the shaft extension 150 is stepped down in diameter to fit within the lumen of adaptor 152 to which it is attached. This attachment may comprise a weld, a bond, an interference fit or other suitable attachment means. The adaptor 152 comprises a braided structure comprising a plurality of wire elements153. This structure is intended to function in a similar fashion to that of a Chinese finger trap—in other words when placed in tension it will grip the proximal end of a clot retrieval shaft such as part 121 of shaft 120 shown in FIG. 27 , provided the part 121 has a slightly larger outer diameter than the inner diameter of the braided adaptor 152.

FIGS. 31 a to 31 d illustrate a clot retrieval device 200 of this invention comprising an extendable shaft. The clot retrieval device 200 comprises a clot engaging portion 201 attached to the distal end of shaft 202. Shaft 202 further comprises a distal region 211, a proximal region 203, and an extension member 205. Extension member 205 fits within the lumen of the tubular proximal region 203, so that it does not interfere with device use in any way unless it is necessary for the shaft to be extended. This necessity might arise in a situation where it was desirable to remove the microcatheter through which the clot retrieval device had been delivered for example, or in a situation where it was desirable to advance a catheter over the shaft of the clot retrieval device which had not been placed in position prior to clot retrieval device delivery.

Shaft 202 may be constructed from a tubular element such as a Nitinol or other metal hypotube, and profiled and/or slotted at points along its length to tailor its flexibility. In another embodiment the proximal region of shaft 202 comprises a hypotube while the distal region211 comprises a tapered wire element.

FIG. 31 a shows the clot retrieval device 200 with the extendable shaft 204 in the non-extended position. FIG. 31 b shows the proximal portion 203 of the shaft 202 of the clot retrieval device 200 with the extension member 204 in the extended position.

FIG. 31 c shows a detailed partially sectioned view of the proximal portion 203 of the shaft 202 of the clot retrieval device 200 with the extension member 204 in the non-extended position. The extension member 204 comprises a proximal end 205 and a distal end 208. The outer diameter of the main body of the extension member is sized to be at least 0.001″and ideally 0.002″ or more smaller than the inner diameter of the proximal shaft 203. The extension member 204 further comprises raised profiles 209 and 210 which are intended to interfere with indentations206 and 207 in the proximal shaft 203. This enables the extension member 204 to be extended to an intermediate length whereby the raised profile210 is positioned between indentations 206 and 207. The profile 210 and the indentations 206 and 207 are configured such that the user can pull the profile 210 past indentation 206 with a moderate amount of force, with this force being greater than that which would be applied to the shaft or extension member during advancement or retraction of a catheter over the shaft or extension member. This intermediate position allows the user to create the scenario described in relation to FIG. 7 , where the shaft length is now sufficiently long to allow the user to safely retract a microcatheter through the tortuous distal region of the anatomy before he/she loses control of the shaft, but not so long as to provide a hindrance to the procedure, which could add to procedural time and patient risk.

The profile 209 is configured such that the user can pull the profile 209 past indentation 206 with a moderate amount of force, but not past indentation 207, which acts as a limit stop preventing complete removal of the extension member from the shaft. This fully extended position allows the user access to a full length shaft extension sufficient to enable him/her to advance a new catheter over the shaft and up to the clot engaging portion of the device without losing control of the device shaft while doing so.

FIG. 31 d shows a detail view of the distal indentation 206 of the proximal region 203 of the shaft 202. This indentation may be formed in a similar manner to that described in relation to FIG. 29 above.

FIGS. 32 a to 32 d illustrate a method of use of a system of this invention to advance a catheter 253 over the shaft of a clot retrieval device 257 after the clot retrieval device has been deployed and the microcatheter through which it was initially delivered has been removed. The method involves the use of a standard guidewire 250, such as the guidewire that might have been used to deliver the microcatheter to the site of the occlusive clot in the first place. Use of a guidewire for this purpose is also described in relation to FIGS. 16 and 17 , and adaptors 260 at the proximal end of the clot retrieval device shaft 259 to permit attachment of a standard guidewire as an extension member are also described previously herein. However a difficulty that can be encountered when using this method is that it can be difficult to introduce a catheter 253 over the floppy distal of a guidewire, as the tip can prolapse and/or snag within the catheter. To solve this problem the guidewire can first be loaded into the catheter by passing the firm proximal end 251 of the guidewire into the proximal end 254 of the catheter, and advancing the guidewire fully through the catheter until the proximal end of the guidewire exits the distal tip 255 of the catheter, as shown in FIG. 32 a.

FIGS. 32 b to 32 d show the next steps of this method, namely: connecting the proximal end 251 of the guidewire to the adaptor 260 on the proximal end of the clot retrieval device shaft, advancing the catheter 253 over the guidewire and on over the clot retrieval device shaft 259 and into the guide catheter or sheath 256, while retaining control of the distal end of the guidewire 252; continuing to advance the catheter 253 over the guidewire and the clot retrieval device shaft until the catheter exits the guide/sheath and reaches the target location, at which point the adaptor should have exited the proximal end of the catheter as shown in FIG. 32 d.

The invention may be utilised in conjunction with any suitable clot retrieval devices such as those described in our WO2012/120490A. In some cases the clot retrieval device comprises an inner elongate body and an outer elongate body which are radially spaced-apart to define a clot receiving space therebetween. The outer elongate body may have large clot receiving openings which are substantially larger than openings in the inner elongate body. Because the device is configured with a long inner expandable member, this member can extend proximal of even a very long clot and upon device deployment the expansion of this member creates a flow channel through the clot, restoring flow to the vascular bed distal of the clot and reducing the pressure gradient across the clot. This reduction in pressure gradient reduces the force required to disengage the clot from the vessel wall and retract it proximally. The scaffolding regions of the outer expandable member expand within the distal portion of the clot applying a compressive force to discrete regions of the clot, thus urging the clot to flow away from these regions, through the inlet openings and into the reception space between the inner and outer members. This causes compression in discrete regions of the clot, but causes minimal compression in regions of the clot, or in the region proximal of the outer member. Minimizing compression on the clot in this way minimizes the forces applied radially outward to the vessel wall, which in turn reduces the frictional force to be overcome when retracting the clot. Because the inner member has created a channel through which blood can pass to the distal vascular bed, the device can be safely left in place for a dwell period prior to withdrawal. This dwell period is desirably greater than one minute and may be as long as 30 minutes or more. Allowing the device to sit in this way allows the clot to flow into the device which facilitates gripping it securely for retrieval. It also allows the distal vascular bed to be gently perfused with fresh oxygenated blood rather than be exposed to a sudden jump in pressure and flow as would be the case if the clot were immediately removed or if the device were to compress the clot so much that a very large flow channel was created upon deployment. Once the dwell period has elapsed the device and microcatheter can be retracted back into either the DAC or guide/sheath. This may be done with the aid of aspiration through the guide/sheath or DAC to assist in retaining a firm grip on the clot and avoiding fragment loss, however the disclosed designs which grip the clot securely and house the clot safely within a reception space and further comprise a distal net or scaffolding region have the advantage that they can be safely used without aspiration. The distal net may be spaced apart from the distal end of the outer member as shown such that it is optimally positioned to trap any fragments released from the clot during retraction even if these fragments originate from that portion of the clot not fully housed with reception space.

It will be apparent from the foregoing description that, while particular embodiments of the present invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the present invention be limited and should be defined only in accordance with the appended claims and their equivalents. 

What is claimed is:
 1. A clot retrieval device comprising: an elongate shaft having a proximal end, a distal end, and a shaft extension member; a clot retrieval element at the distal end of the elongate shaft, a proximal end of the elongate shaft configured to retract a first catheter over the elongate shaft, the shaft extension member comprising one or more raised profiles configured to interfere with one or more indentations along the elongate shaft such that the shaft extension member is configured to extend between a first length and an intermediate length; and a second catheter being advanceable to or adjacent to the distal end of the elongate shaft for enhanced aspiration adjacent to the clot retrieval element.
 2. The clot retrieval device as claimed in claim 1, wherein a first indentation along the elongate shaft is configured to allow a first raised profile on the shaft extension member to pass by in a distal direction, thereby extending the shaft extension member between the first length and the intermediate length.
 3. The clot retrieval device as claimed in claim 2, wherein a second indentation along the elongate shaft is configured to prevent a second raised profile on the shaft extension member to pass by in a distal direction, thereby preventing the shaft extension member from extending beyond a final length, wherein the second indentation is positioned distal the first indentation.
 4. The clot retrieval device as claimed in claim 1, wherein aspiration is delivered through the second catheter, a lumen of the second catheter being larger than a lumen of the first catheter.
 5. The clot retrieval device as claimed in claim 4, wherein the first catheter comprises a microcatheter through which the clot retrieval device is delivered and the second catheter is an intermediate catheter.
 6. The clot retrieval device as claimed in claim 1, wherein the proximal end of the elongate shaft is adapted for retraction of the first catheter having a lumen and subsequent advancement of the second catheter having a lumen, wherein the lumen of the second catheter is larger than the lumen of the first catheter.
 7. The clot retrieval device as claimed in claim 1, wherein the proximal end of the elongate shaft is adapted for retraction and removal of the first catheter having a lumen through the second catheter.
 8. The clot retrieval device as claimed in claim 1, further comprising: an adaptor at the proximal end of the elongate shaft of the clot retrieval device, the adaptor being adapted to receive the shaft extension member.
 9. The clot retrieval device as claimed in claim 8, wherein the adaptor is integral with the clot retrieval device shaft proximal end, and wherein the adaptor comprises a receiver which is adapted to receive the shaft extension member.
 10. The clot retrieval device as claimed in claim 8, wherein the adaptor is releasably mountable to the proximal end of the elongate shaft.
 11. The clot retrieval device as claimed in claim 10, wherein the adaptor comprises a mounting section for mounting to the proximal end of the shaft and a receiver which is adapted to receive the shaft extension member.
 12. The clot retrieval device as claimed in claim 11, wherein the mounting section is a push fit with the proximal end of the elongate shaft, and wherein the receiver is a push fit with the shaft extension member.
 13. The clot retrieval device as claimed in claim 1, wherein the elongate shaft has at least one tactile feature at or adjacent to the proximal end thereof.
 14. The clot retrieval device as claimed in claim 1, wherein the clot retrieval device shaft has at least one high friction feature at or adjacent to the proximal end thereof.
 15. The clot retrieval device as claimed in claim 1, wherein one or both of the proximal end and the extension member comprises at least one stop to set the length to which the extension member may extend from the tubular proximal end and/or to control the degree of push that applicable to the extension member.
 16. A clot retrieval system comprising: a clot retrieval device as claimed in claim 1; and an adaptor for mounting to the proximal end of the elongate shaft of the clot retrieval device.
 17. The clot retrieval system as claimed in claim 16, wherein the adaptor comprises a mounting section for mounting to the proximal end of the clot retrieval device shaft and a receiver which is adapted to receive the shaft extension member, and wherein the adaptor mounting section is a push fit with the proximal end of the clot retrieval shaft.
 18. The clot retrieval system as claimed in claim 17, wherein the adaptor receiver is a push fit with the shaft extension member, and/or wherein the adaptor is configured to accept the proximal end of a standard guidewire.
 19. A method for retrieving a clot from a vasculature comprising: positioning a second catheter over a first catheter; providing a clot retrieval device comprising an elongate shaft comprising one or more indentations and a shaft extension member comprising one or more raised profiles; pushing the shaft extension member such that the one or more raised profiles interferes with the one or more indentations, thereby extending the shaft extension member between a first length and an final length; deploying the clot retrieval device from the first catheter; and retracting the first catheter over the shaft and maintaining control of a proximal end of the shaft.
 20. The method as claimed in claim 19, further comprising: applying aspiration to the clot through a lumen of the second catheter after retraction of the first catheter over the clot retrieval device elongate shaft, wherein the first catheter is a delivery catheter for the clot retrieval device and the method further comprises deploying the clot retrieval device from the delivery catheter and subsequently retracting the delivery catheter over the clot retrieval device shaft. 